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IRC R401.3 requires a minimum 5% slope (6 inches drop in the first 10 feet) away from the foundation.

Key details:

Measurement: 6" vertical drop measured horizontally 10' out from the foundation wall.
Impervious surfaces (patios, walks, driveways): Only 2% slope (1/4" per foot) required (R401.3 Exception).
Swales: If lot lines/walls prevent 10' of slope, a swale/drain is required to carry water away (R401.3).
Backfill: Must be free of organic material/debris, compacted in lifts to prevent settlement that reverses slope (R403.1.6).

Practical tips:

Establish rough grade before pouring flatwork so you hit the 5% on dirt and 2% on concrete simultaneously.
Compact the 10' zone thoroughly (mechanical plate compactor, not just track-walking). Settlement is the #1 callback.
Verify with a 10' straightedge and level (or laser/transit) before sod. A 6" gap under the level at 10' = pass.
Window wells/steps: Grade must still slope away; use drains in wells tied to footing drain.

Check local amendments. Some jurisdictions require 6% or 10' minimum impervious surface extension. Always confirm with the AHJ before final inspection.

Most residential building codes, including the International Residential Code (IRC), require a minimum slope away from the foundation to ensure proper drainage and prevent water intrusion.

IRC Section R401.3 states: > “The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than 5 percent (6 inches of fall in 10 feet) for a minimum distance of 10 feet measured perpendicular to the foundation wall.”

If physical obstructions (like property lines, walls, or slopes) prevent achieving the full 10-foot slope, the code allows an alternative: > “Where lot lines, walls, slopes, or other physical barriers prohibit 10 feet of horizontal distance, a 5 percent slope shall be provided to an approved alternative method of diverting water away from the foundation.” (IRC R401.3 Exception)

Key practical points for sod installation:

Ensure the subgrade is compacted and graded to this slope before placing topsoil and sod.
Topsoil should be uniform (typically 4–6 inches deep) and not alter the intended slope.
Avoid creating low spots or depressions near the foundation where water can pool.
Downspouts should extend at least 5 feet from the foundation (IRC R801.3) and discharge onto graded surfaces, not directly into the soil near the wall.

Note: Always check local amendments — some jurisdictions may require greater slope (e.g., 10%) or longer distances, especially in expansive soil or high-rainfall areas. When in doubt, consult your local building department or a licensed civil engineer/landscaper. Improper grading is a leading cause of basement leaks and foundation damage.

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